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Data Entry Blunders Force Air Asia Pilots To Land in Melbourne Instead of Malaysia (mashable.com)
A flight from Sydney to Malaysia ended up in Melbourne after the captain incorrectly entered the plane's location in its navigation system just before take-off, according to a safety investigation, whose conclusion was published this week. Mashable reports:The Air Asia pilots made several errors in entering data into the aircraft's navigation system, which caused them to follow an incorrect flight path out of Sydney, according to Australian transportation officials. While troubleshooting the incorrect flight path, the pilots were unable to fix the issue, and may have compounded it. The aircraft's systems would not allow the plane to be flown in instrument conditions and the weather also had deteriorated in Sydney by the time the pilots decided to turn back. They were directed via radar to a visual approach in Melbourne where they could land safely. The pilots did not believe the airport was located in Malaysia.
This is because the paragraph above was posted as a correction to the article.
Otherwise the article gives the impression that the pilots were so incompetent as to not even realise which country they were in.
systemd is Roko's Basilisk.
OK, here's what really happened:
The captain entered the wrong coordinates into the Inertial Reference System, which is the airplane's primary reference for position. Normally, there are several ways the system could have detected this:
- It is normally updated by GPS, but if the difference between the two is too large, the sytem considers the GPS to be faulty. Some warning messages were given, but these warnings often occur during normal operation on the ground and then disappear afterwards, so pilots are sort of "trained" by experience to disregard them.
- When applying take-off thrust, the system normally realigns to the coordinates of the runway. But, thanks to genius Airbus programming as usual, the system did not perform the update because the error was too large.
- If an incorrect latitude is entered, the system can detect the error because it measures the earth's rotation vector and the gravity vector during IRS alignment while the airplane is still parked. In this case the longitude was incorrect, which cannot be detected by the system. The earth rotates the same at any longitude.
After Take-off, two problems arose:
1. The position was way off, the plane actually thought it was somewhere close to South Africa
2. The Enhanced Ground Proximity Warning System activated, yelling "Terrain, terrain!", based on the incorrect position (not a big problem, but confusing as hell and creating extra stress for the pilots).
3. The heading indication was incorrect, because the IRS internally knows only the true heading (relative to true north) while heading indications on aircraft systems are relative to magnetic north for historical reasons. The IRS converts between the two using local magnetic variation (the difference between magnetic north and true north) but, because it thought it was near South Africa, it used the wrong value for the variation and therefore displayed an incorrect magnetic heading. This caused the autopilot to turn the wrong way.
The pilots, fearing that something was wrong with the entire Air Data Reference system, applied a procedure for unreliable airspeed (they did not know which instruments they could trust anymore) and turned off two of the three ADR computers. This resulted in a further loss of information displayed on their screens which was not exactly helpful to their situation. The procedure exists to disable certain safety protections that might accidentally activate based on erroneous data (if two of the three computers say the airplane is stalling, the flight control computers will push the nose down and override the pilots' sidesticks) but in this case this procedure was not necessary and actually made their life harder.
Now, if you've lost half your instruments, you don't know which instruments you can trust and which you can't (with the heading being wrong for certain), it's not a good idea to fly on instruments through clouds at low altitude. Certainly not an approach to a runway without being able to see it. So they needed to go to an airport where the visibility and cloud base allowed a visual landing. The closest suitable airport with good weather was Melbourne, so that's where they went.